Active energy ray curable compositions are used as hard coating agents for plastic substrates of home electric products, cellular phones, etc. because of the characteristics of a little heat history applied to coating substrates and excellent coating hardness and scratch resistance. An example of the active energy ray curable compositions is an active energy ray curable composition (solvent-type active energy ray curable composition) containing an acryl acrylate polymer having a polymerizable unsaturated double bond and a polymer not having an unsaturated double bond such as a polymerizable acrylic resin, a polymerizable monomer, and an organic solvent used as a diluent. For example, when this active energy ray curable composition is used as a coating material for spray coating, it is necessary for the coating material to contain the organic solvent in a large amount of 50 to 90% by mass. Therefore, when cured coating films are formed on surfaces of substrates such as plastic and the like by using an active energy ray curable coating material containing the resin composition, the organic solvent in the coating material is evaporated, thereby causing the problem of worsening working environments. The evaporated organic solvent also causes air pollution.
In contrast, an active energy ray curable aqueous resin composition (for example, refer to Patent Literatures 1 and 2) using water, not an organic solvent, as a diluent is proposed. The active energy ray curable aqueous resin composition is made aqueous by neutralizing acid groups such as a carboxyl group and the like introduced into a resin with ammonia or organic amine to impart water solubility and dispersibility to the resin. However, the resin made aqueous by neutralizing the acid groups has poor storage stability, and thus has the problem of partial separation of the active energy ray curable aqueous resin composition and the problem of easily producing failures such as cissing, whitening, or the like in cured coating films of the composition.
Accordingly, there is demand for an active energy ray curable aqueous resin composition having excellent storage stability and high transparency and being capable of forming cured coating films with excellent appearances.